Historically, misdiagnosis rates have been high due to the complex nature of the disorder although some research now indicates that misdiagnosis may be reducing.

The International Classification of Disease (ICD-11) which is due to be finalised in 2017 will have functional disorders within the neurology section for the first time.

The psychological mechanism of conversion can be the most difficult aspect of a conversion diagnosis. Even if there is a clear antecedent trauma or other possible psychological trigger, it is still not clear exactly how this gives rise to the symptoms observed. Patients with medically unexplained neurological symptoms may not have any psychological stressor, hence the use of the term "functional neurological symptom disorder" in DSM-V as opposed to "conversion disorder", and DSM-V's removal of the need for a psychological trigger.

Treatment may involve investigation, reassurance and explanation, and possibly specialist treatment such as antidepressants or cognitive behavioral therapy.

Empirical studies have found that the prognosis for conversion disorder varies widely, with some cases resolving in weeks, and others enduring for years or decades. There is also evidence that there is no cure for Conversion Disorder, and that although patients may go into remission, they can relapse at any point. Furthermore, many patients who are 'cured' continue to have some degree of symptoms indefinitely.

Functional somatic syndromes may occur in 6 to 36% of the population.

Whether a given medical condition is termed a "functional disorder" depends in part on the state of knowledge. Some diseases, including epilepsy, schizophrenia, and migraine headaches were once considered functional disorders, but are no longer generally classified that way.

Irritable Bowel Syndrome (IBS),

Fibromyalgia (FMS),

Chronic Fatigue Syndrome (CFS),

Chronic Pelvic Pain (CPP),

Interstitial Cystitis (IC),

Temporomandibular Joint Pain (TMJ), Functional Neurological Symptom Disorder (FNsD),

Non-Cardiac Chest Pain (NCCP),

Post-Traumatic Stress Disorder (PTSD),

Dysuria (Pain On Urination),

and Multiple Chemical Sensitivity

In 2010, the American College of Rheumatology approved provisional revised diagnostic criteria for fibromyalgia that eliminated the 1990 criteria's reliance on tender point testing. The revised criteria use a widespread pain index (WPI) and symptom severity scale (SS) in place of tender point testing under the 1990 criteria. The WPI counts up to 19 general body areas in which the person has experienced pain in the preceding two weeks. The SS rates the severity of the person's fatigue, unrefreshed waking, cognitive symptoms, and general somatic symptoms, each on a scale from 0 to 3, for a composite score ranging from 0 to 12. The revised criteria for diagnosis are:

- WPI ≥ 7 and SS ≥ 5 "OR" WPI 3–6 and SS ≥ 9,

- Symptoms have been present at a similar level for at least three months, "and"

- No other diagnosable disorder otherwise explains the pain.

There is no single test that can fully diagnose fibromyalgia and there is debate over what should be considered essential diagnostic criteria and whether an objective diagnosis is possible. In most cases, people with fibromyalgia symptoms may also have laboratory test results that appear normal and many of their symptoms may mimic those of other rheumatic conditions such as arthritis or osteoporosis. The most widely accepted set of classification criteria for research purposes was elaborated in 1990 by the Multicenter Criteria Committee of the American College of Rheumatology. These criteria, which are known informally as "the ACR 1990", define fibromyalgia according to the presence of the following criteria:

- A history of widespread pain lasting more than three months – affecting all four quadrants of the body, i.e., both sides, and above and below the waist.

- Tender points – there are 18 designated possible tender points (although a person with the disorder may feel pain in other areas as well). Diagnosis is no longer based on the number of tender points.

The ACR criteria for the classification of patients were originally established as inclusion criteria for research purposes and were not intended for clinical diagnosis but have now become the "de facto" diagnostic criteria in the clinical setting. It should be noted that the number of tender points that may be active at any one time may vary with time and circumstance. A controversial study was done by a legal team looking to prove their client's disability based primarily on tender points and their widespread presence in non-litigious communities prompted the lead author of the ACR criteria to question now the useful validity of tender points in diagnosis. Use of control points has been used to cast doubt on whether a person has fibromyalgia, and to claim the person is malingering; however, no research has been done for the use of control points to diagnose fibromyalgia, and such diagnostic tests have been advised against, and people complaining of pain all over should still have fibromyalgia considered as a diagnosis.

A neurological disorder is any disorder of the nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord or other nerves can result in a range of symptoms. Examples of symptoms include paralysis, muscle weakness, poor coordination, loss of sensation, seizures, confusion, pain and altered levels of consciousness. There are many recognized neurological disorders, some relatively common, but many rare. They may be assessed by neurological examination, and studied and treated within the specialities of neurology and clinical neuropsychology.

Interventions for neurological disorders include preventative measures, lifestyle changes, physiotherapy or other therapy, neurorehabilitation, pain management, medication, or operations performed by neurosurgeons. The World Health Organization estimated in 2006 that neurological disorders and their sequelae (direct consequences) affect as many as one billion people worldwide, and identified health inequalities and social stigma/discrimination as major factors contributing to the associated disability and suffering.

Although the brain and spinal cord are surrounded by tough membranes, enclosed in the bones of the skull and spinal vertebrae, and chemically isolated by the blood–brain barrier, they are very susceptible if compromised. Nerves tend to lie deep under the skin but can still become exposed to damage. Individual neurons, and the neural networks and nerves into which they form, are susceptible to electrochemical and structural disruption. Neuroregeneration may occur in the peripheral nervous system and thus overcome or work around injuries to some extent, but it is thought to be rare in the brain and spinal cord.

The specific causes of neurological problems vary, but can include genetic disorders, congenital abnormalities or disorders, infections, lifestyle or environmental health problems including malnutrition, and brain injury, spinal cord injury or nerve injury. The problem may start in another body system that interacts with the nervous system. For example, cerebrovascular disorders involve brain injury due to problems with the blood vessels (cardiovascular system) supplying the brain; autoimmune disorders involve damage caused by the body's own immune system; lysosomal storage diseases such as Niemann-Pick disease can lead to neurological deterioration. The National Institutes of Health recommend considering the evaluation of an underlying celiac disease in people with unexplained neurological symptoms, particularly peripheral neuropathy or ataxia.

In a substantial minority of cases of neurological symptoms, no neural cause can be identified using current testing procedures, and such "idiopathic" conditions can invite different theories about what is occurring.

CMM has clear severe impacts on a patient’s ability to carry out daily manual tasks. It is recommended that children be placed under more forgiving school environments, allowing more time for written evaluations and limiting handwritten assignments, to ease the burden of the movement disability. Furthermore, because of patients’ inability to perform pure unilateral movements and their difficulty with tasks requiring skilled bimanual coordination, young and new members to the workforce are encouraged to consider professions that do not require complex bimanual movements, repetitive or sustained hand movements, or extensive handwriting, to reduce overuse, pain, and discomfort in upper limbs.

Because of its pronounced and obviously noticeable signs and symptoms, CMM patients can suffer social stigma, however physicians need to make it clear to parents, family, and friends that the disorder bears no relation to intellectual abilities. However, the rarity of this neurologic disease, found in one in a million people, makes its societal and cultural significance quite limited.

Functional weakness is weakness of an arm or leg due to the nervous system not working properly. It is not caused by damage or disease of the nervous system. Patients with functional weakness experience symptoms of limb weakness which can be disabling and frightening such as problems walking or a ‘heaviness’ down one side, dropping things or a feeling that a limb just doesn’t feel normal or ‘part of them’. Functional weakness may also be described as functional neurological symptom disorder (FNsD), Functional Neurological Disorder (FND) or functional neurological symptoms. If the symptoms are caused by a psychological trigger, it may be diagnosed as 'dissociative motor disorder' or conversion disorder (CD).

To the patient and the doctor it often looks as if there has been a stroke or have symptoms of multiple sclerosis. However, unlike these conditions, with functional weakness there is no permanent damage to the nervous system which means that it can get better or even go away completely.

The diagnosis should usually be made by a consultant neurologist so that other neurological causes can be excluded. The diagnosis should be made on the basis of positive features in the history and the examination (such as Hoover's sign). It is dangerous to make the diagnosis simply because tests are normal. Neurologists usually diagnose wrongly about 5% of the time (which is the same for many other conditions.)

Many patients with functional weakness suffer from not being believed. Although psychological factors can be important for a some patients, for the majority of individuals the cause of their weakness has a physical trigger such as a virus, injury or other medical condition. The symptoms of functional weakness are real, and are as disabling and distressing as Multiple Sclerosis or Parkinson's.

The most effective treatment is physiotherapy, however it is also helpful for patients to understand the diagnosis, and some may find CBT helps them to cope with the emotions associated with being unwell. For those with conversion disorder, psychological therapy is key to their treatment as it is emotional or psychological factors which are causing their symptoms.

There is considerable research into the causes, diagnosis and treatments for FGIDs. Diet, microbiome, genetics, neuromuscular function and immunological response all interact. Heightened mast cell activation has been proposed to be a common factor among FGIDs, contributing to visceral hypersensitivity as well as epithelial, neuromuscular, and motility dysfunction.

Currently, clinical diagnosis of CMM disorder has been based on clinical findings or molecular genetic testing.

"Clinical Findings (Signs and Symptoms)"""":"

- onset of mirror movements in infancy or early childhood

- persistence of mirror movements into and throughout adulthood with the absence of other neurologic disorders

- little improvement nor deterioration of mirror movements over the course of one’s life

- intensity of mirrored movements increasing with the complexity of the voluntary movement

- involuntary mirror movements that are generally of lesser amplitude compared with voluntary movements

- predominant mirror movement in upper limbs, with increasing severity in more distal appendages (fingers)

- inability to perform tasks requiring skilled bimanual coordination

- occasional pain in the upper limbs during prolonged manual activities

- occasional observed subclinical mirroring movement, but detectable with accelerometer gloves

"Molecular genetic testing"":"

- identification of a heterozygous mutant "DCC, DNAL4, or RAD51" gene (single gene test or multi-gene panel)

Brain imaging (functional/structural MRI) may help direct the search for microscopic abnormalities in brain structure and function responsible for late life depression. Ultimately, imaging technologies may serve as tools for early diagnosis and subtyping of depression.

Despite recent initiatives to study psychopathology along dimensions of behavior and neurobiological indices, which would help refine a clearer picture of the development and treatment of externalizing disorders, the majority of research has examined specific mental disorders. Thus, best practices for many externalizing disorders are disorder-specific. For example, substance use disorders themselves are very heterogeneous and their best-evidenced treatment typically includes cognitive behavioral therapy, motivational interviewing, and a substance disorder-specific detoxification or psychotropic medication treatment component. The best-evidenced treatment for childhood conduct and externalizing problems more broadly, including youth with ADHD, ODD, and CD, is parent management training, a form of cognitive behavioral therapy. Additionally, individuals with ADHD, both youth and adults, are frequently treated with stimulant medications (or alternative psychotropic medications), especially if psychotherapy alone has not been effective in managing symptoms and impairment. Psychotherapy and medication interventions for individuals with severe, adult forms of antisocial behavior, such as antisocial personality disorder, have been mostly ineffective. An individual's comorbid psychopathology may also influences the course of treatment for an individual.

ADHD often precedes the onset of ODD, and approximately half of children with ADHD, Combined Type also have ODD. ODD is a risk factor for CD and frequently precedes the onset of CD symptoms. Children with an early onset of CD symptoms, with at least one symptom before age 10 years, are at risk for more severe and persistent antisocial behavior continuing into adulthood. Youth with early-onset conduct problems are particularly at risk for ASPD (note that an onset of CD prior to age 15 is part of the diagnostic criteria for ASPD), whereas CD is typically limited to adolescence when youth's CD symptoms begin during adolescence.

The person's appearance, behavior, and history, along with a psychological evaluation, are usually sufficient to establish a diagnosis. There is no test to confirm this diagnosis. Because the criteria are subjective, some people may be wrongly diagnosed.

Physical examination can rule out anismus (by identifying another cause) but is not sufficient to diagnose anismus.

For diagnosis, measures of liver biochemistry and pancreatic enzymes are performed. Along with ruling out structural abnormalities, normally by performing an abdominal ultrasound and endoscopic retrograde cholangiopancreatography (ERCP). Measurements of bile transit when performing ERCP are taken to help evaluate different treatment options.

Sphincter of Oddi dysfunction is best diagnosed using manometry-an internal test done to measure the pressures within surrounding ducts to determine whether or not the muscle is functioning normally.

Functional gastrointestinal disorders are very common. Globally, irritable bowel syndrome and functional dyspepsia alone may affect 16–26% of the population.

Giveway weakness (also "give-away weakness", "collapsing weakness", etc.) refers to a symptom where a patient's arm, leg, can initially provide resistance against an examiner's touch, but then suddenly "gives way" and provides no further muscular resistance.

Treatment of ALS2-related disorders includes physical therapy and occupational therapy to promote mobility and independence and use of computer technologies and devices to facilitate writing and voice communication.